Current approaches for obtaining pressure and other information from the flow of air over airfoils and other surfaces utilize “port” holes in the airfoil surface. From these holes, individual tubes convey the pressure to a central location. The tubes, pressure registration components, and other data-acquisition devices are complex, weighty, and require clear space for routing them through the airfoil. Moreover, such runs of tubing and connections have a myriad of potential failure points, including pinched tubes, holes, seal leaks, faulty electrical connections, etc. Installation of such a pressure-measurement system also can require a significant amount of labor. As a result, for pressure profiling a model of a commercial aircraft, for example, the cost for the test can exceed half a million dollars for this portion of the work alone.
Other approaches seek to utilize pressure-sensitive films applied to wings. These films provide qualitative data, but cannot provide accurate quantitative data as to the pressure distribution and behavior. Additionally, a responsiveness of the films is limited, and permanent data acquisition using the films is challenging to implement.
One approach proposes a pressure-sensing method, which incorporates sensing channels for a fluid connected to “pressure-sensing modules.” Data from these modules is described as being provided to a “signal processing” module via wired or wireless connection. Moreover, the approach places units having varying heights from three to ten millimeters on an existing airfoil. At higher wind speeds, millimeter-scale deviations are significant, especially on smaller airfoils such as are used in testing and development models. In particular, as wind speeds increase, a maximum allowable deviation decreases drastically. For example, even at speeds of only forty meters per second (about ninety miles per hour), a “trip”—a piece of tape with widely spaced sandy grit of about 0.75 mm in diameter embedded on it—produces very noticeable changes in turbulent versus laminar flow when applied to a leading wing edge. These changes are at least in part due to an irregular profile of the trip. Small deviations on the scale of a millimeter, or even up to three millimeters, may be acceptable for profiles that are very smooth and under the right circumstances.
Another approach proposes a flat pressure sensor device which runs miniature resin pipes to a pressure converter and measurement device inside a wing. As with previous approaches, this approach proposes placement of a millimeter-scale object in the airflow, and utilizes multiple tubes, each of which presents a potential point of failure or mis-manufacture. Still another approach uses pressure belts, which are flat sensor modules three millimeters thick adhered to a surface of an aircraft. These pressure belts can provide reasonable performance, but require wired power and data connections, each of which provides an additional point of failure and requires direct modification of the airfoil.